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The Ten-Volt Blues

nomadradio

Analog Retentive
Apr 3, 2005
5,562
8,197
573
Louisville, KY
www.nomadradio.com
The 10-Volt Blues.

This refers to a pattern of failures found in solid-state CB radios that get to be 20 or more years old.

These radios are packed with dozens of small aluminum-electrolytic capacitors. This type part is irresistible to the product's designer. Does a really good job in a small package, and at low cost. Just one drawback. They get old and fail.

Twenty or more years down the road. Joe design engineer doesn't care about that.

The most-evident pattern that emerges after repairing the first few hundred of these failures is that the caps with the lowest voltage rating tend to fail first. Must have something to do with the chemistry inside these parts, but that's not my department.

What we learned to do was replace the whole "family" of 6- and 10-Volt rated caps any time the first one of them goes bad in that radio. And you'll find production changes. A Cobra 142 made in one year might have a 10-Volt cap in a spot where you see a 16-Volt part in radios made 5 years later.

One cap that goes bad will kill the receiver's audio only. The S-meter still kicks around on channel noise, and transmit side is not affected at all.

Another one causes the AM transmit audio to squeal when the carrier power is turned down.

Yet another will kill all your transmit, AM and SSB both, but leave the receiver unaffected.

Probably the worst one of the bunch will cut the transmit power in half or less. The only immediate clue will be that the final's bias current remains zero no matter the bias-trimpot settting.

The life of these parts may extend to 40 years or more. And that 20-year mark is not a minimum, by any means. The operating temperature of these parts will have an influence. Mileage is a big deal, but there is no odometer on a radio to see how many thousand hours of heat stress have been put onto the parts inside.
A 20 year-old radio that's new in the box probaby won't have any failed caps. And a radio that was turned on and run 24/7 for 15 years is a lot likelier to exhibit the 10-Volt Blues.

One odd pattern that emerged was the "spare radio on the shelf" failure. Typical example was a Uniden-made 40-channel SSB CB like a Madison or Washington that was used for 15 or 20 years. When it got replaced by a bigger "black" radio like a Galaxy or RCI, this one goes on the shelf as the spare base station.
And there it sits for 3, 4 or maybe 5 years until the big radio takes a dump and goes out for repairs. The spare radio comes off the shelf and gets powered up for the first time in several years.

It lasts for a week or less, and one of the symptoms above appears.

And that's the pattern. A well-used radio lasts only a week or less after a long shelf visit and then quits.

My favorite of all the 10-Volt Blues failures is the cap that burns out the coil in your speaker and the audio chip both when it fails as a short circuit.

The cool part is when someone leaves that shorted cap in the radio and replaces the audio chip and speaker. The chemistry in the failed cap sometimes causes the short to go away. But only for a while. Even if the person doing the repair were to "test" this cap it would show okay.

Until it shorts again and blows out the speaker and audio chip.

Again.

That part is one we learned to just change in any radio over 25 years old, whether it checks bad or not.
Cheap insurance.

73
 

loosecannon

Sr. Member
Mar 9, 2006
4,216
3,644
273
great write up Nomad.

I'm really glad you decided to turn your attention to this forum, and this article is just one reason why.

People tend to send me old uniden chassis most of the time, and since i do more restorations than actual repairs, i always tell them that a 30 year old radio is not "restored" until the electrolytics have been replaced.

sure, i could just replace the likely culprits, but i feel bad when someone has to pay to ship a radio to me a second time, so i tend to suggest the whole re-cap.

I am also seeing a lot more bad "tubular caps" in the tuning cans than i used to, and i remember years ago you were warning about this.

seems like we might have hit the time frame where these are starting to go more often.
I, like you, use trimmer caps on the bottom of the board to fix these. thank goodness i haven't seen any go short yet!

Since the 148 is in current production, i need to find a source for the tuning cans themselves and buy a few sets. (if anyone knows a place, let me know)

One thing people need to know if they are going to re-cap their own radio is that you can't just go off of the parts list for the values in your radio.

always buy a few extra of each value in case you find a cap in a radio that isn't what the parts list says it should be.
you want to replace it with the value that was in the radio.

as an example, there is a cap in the S meter circuit of the 8719 chassis that calls for a .22uf electrolytic (that's point 22) and i have never seen that value there.
it's usually a .47 in that spot, and i have even seen a 1uf there in some chassis.

my guess is that it depends on the characteristics of the actual meter used in the radio, and if you replace this part with a different value, your meter is going to act funny.
LC
 

Shadetree Mechanic

808 On The North Side of Dover
Oct 23, 2017
5,003
8,044
673
50
The First State (Delaware)
Good stuff here. I am trying to get set up to re cap some radios myself. I have a teenage son that is ok at soldering, but I am going to get him this kit / lesson before I turn him loose on a radio.



http://www.vectronics.com/Product.php?productid=VEC-1500K

If you click on the downloads, you can get the lesson for free.
Thanks for the write up Nomadradio.
 

Robb

Yup
Dec 18, 2008
11,433
3,580
323
Silicon Valley CA, Storm Lake IA
The 10-Volt Blues.

This refers to a pattern of failures found in solid-state CB radios that get to be 20 or more years old.

These radios are packed with dozens of small aluminum-electrolytic capacitors. This type part is irresistible to the product's designer. Does a really good job in a small package, and at low cost. Just one drawback. They get old and fail.

Twenty or more years down the road. Joe design engineer doesn't care about that.

The most-evident pattern that emerges after repairing the first few hundred of these failures is that the caps with the lowest voltage rating tend to fail first. Must have something to do with the chemistry inside these parts, but that's not my department.

What we learned to do was replace the whole "family" of 6- and 10-Volt rated caps any time the first one of them goes bad in that radio. And you'll find production changes. A Cobra 142 made in one year might have a 10-Volt cap in a spot where you see a 16-Volt part in radios made 5 years later.

One cap that goes bad will kill the receiver's audio only. The S-meter still kicks around on channel noise, and transmit side is not affected at all.

Another one causes the AM transmit audio to squeal when the carrier power is turned down.

Yet another will kill all your transmit, AM and SSB both, but leave the receiver unaffected.

Probably the worst one of the bunch will cut the transmit power in half or less. The only immediate clue will be that the final's bias current remains zero no matter the bias-trimpot settting.

The life of these parts may extend to 40 years or more. And that 20-year mark is not a minimum, by any means. The operating temperature of these parts will have an influence. Mileage is a big deal, but there is no odometer on a radio to see how many thousand hours of heat stress have been put onto the parts inside.
A 20 year-old radio that's new in the box probaby won't have any failed caps. And a radio that was turned on and run 24/7 for 15 years is a lot likelier to exhibit the 10-Volt Blues.

One odd pattern that emerged was the "spare radio on the shelf" failure. Typical example was a Uniden-made 40-channel SSB CB like a Madison or Washington that was used for 15 or 20 years. When it got replaced by a bigger "black" radio like a Galaxy or RCI, this one goes on the shelf as the spare base station.
And there it sits for 3, 4 or maybe 5 years until the big radio takes a dump and goes out for repairs. The spare radio comes off the shelf and gets powered up for the first time in several years.

It lasts for a week or less, and one of the symptoms above appears.

And that's the pattern. A well-used radio lasts only a week or less after a long shelf visit and then quits.

My favorite of all the 10-Volt Blues failures is the cap that burns out the coil in your speaker and the audio chip both when it fails as a short circuit.

The cool part is when someone leaves that shorted cap in the radio and replaces the audio chip and speaker. The chemistry in the failed cap sometimes causes the short to go away. But only for a while. Even if the person doing the repair were to "test" this cap it would show okay.

Until it shorts again and blows out the speaker and audio chip.

Again.

That part is one we learned to just change in any radio over 25 years old, whether it checks bad or not.
Cheap insurance.

73
Ya nailed it . . .
 
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